The invention relates to a thread clamp for a rapier head and to a rapier head having a thread clamp of this kind as well as to a rapier weaving machine with a thread clamp of this kind or with a rapier of this kind.
In rapier weaving machines the weft thread is inserted into a shed by means of an inserting rapier, which is mounted on a bar or on a flexible band and is taken over at a transfer point in the central part of the shed by a receiving rapier and further forwarded. The inserting rapier has the task of reliably gripping the presented weft thread, of inserting the latter into the shed and of guiding it precisely to the receiving rapier. Each rapier includes a rapier head with a thread clamp in order to be able to firmly clamp the weft thread during the weft insertion. In the case of automatically clamping thread clamps the thread transfer takes place through drawing the weft thread respectively in or out of previously set clamping regions of the respective thread clamps. For the manufacture of cloths with weft yarns of different thicknesses or with weft yarns of different smoothness, controlled thread clamps can be used in one or both rapier heads, with the thread clamp of the inserting rapier being actively opened or that of the receiving rapier being actively closed during the thread transfer.
The controlled thread clamps can be controlled mechanically and/or electrically. An electrically controlled thread clamp with an electrical actuator is for example described in the publication WO 99/60193. The power supply for the controlled thread clamp takes place via an induction coil which is arranged in the rapier head and which is coupled inductively to a second induction coil which is mounted above the shed. The thread clamp which is described in WO 99/60193 includes a movable clamping part which is held closed by means of a prestressed spring. An electromagnet in the actuator serves for the opening of the clamping part. The disadvantage of this arrangement is that the electromagnet must be supplied with power in order to keep the thread clamp open, which can lead to an undesirable heating up of the electromagnet and of the other current carrying parts. The electrical energy consumption of this thread clamp is therefore comparatively high, even if the opening times of the thread clamp are short in relation to the entire weft insertion cycle.